JPH0635199B2 - Thermal transfer ribbon - Google Patents

Abstract

A thermal transfer ribbon including a resistive heating element layer having a thermally transferable ink layer on the front side thereof is provided with a thermally sensitive indicator layer on the back side thereof. Heat generated in the resistive layer fuses the ink which transfers selectively to record grey scale image defining dots of various sizes on an ink receiving sheet in contact with the ink layer. The heat generated in the resistive layer also flows to the indicator layer to form corresponding indicator marks which are proportional to the recorded dots. The indicator marks are visible on the back side of the ribbon and are optionally monitored to provide feed back to a thermal system for accurately controlling the density of pixel area defining the recorded image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermal printing or recording, and more particularly to thermal transfer ribbons for use in recording toned or grayscale images on ink receiving paper.

Japanese Patent Application No. 60-268274, Japanese Patent Application No. 60-24380
No. 7 and Japanese Patent Application No. 60-243808 disclose a closed loop system and method for thermally recording a tone or grayscale image defined by an electronic image signal on a thermal paper or transparent material containing an integral thermal recording layer. Has been done.

The recorded image is formed by a matrix array of a large number of minute pixel areas each having a desired target density or tone specified by the image signal. The tone of each pixel area is changed by changing the size of the dots recorded therein in a manner similar to halftone lithographic printing.

The nature of the thermosensitive recording layer is such that it gradually increases with the increase in the amount of heat energy applied to form the dots.
In order to precisely control the dot size, the thermal recording system disclosed in the above application uses a closed loop control system to optically monitor the pixel density by controlling the pixel density during the formation of the dot. . This information is fed back to the control system where it is compared with the signal indicative of the target density. Based on this comparison, the control system adjusts the application of thermal energy and gradually increases the dot size until a predetermined comparison value is reached. After that, the application of heat energy ends.

The key point for precise control of pixel density is the optical monitoring device,
That is, to configure the recording device so that the photodetector has an uninterrupted dot-forming field of view to provide the necessary feedback.

When the recording medium is a thermal paper having an opaque base sheet, heat energy is preferably applied by a thermal printing head from the back side of the thermal paper through the base as disclosed in Japanese Patent Application No. 60-268274. Forming dots in the recording layer from which the dot formation can be monitored without being interrupted by the print heads. When the recording medium is a transparent material, the above-mentioned Japanese Patent Application No.
No. 0-243807 and Japanese Patent Application No. 60-243805, heat from the printing head is applied through the light-reflective buffer sheet engaging with the front surface of the recording layer, and the light is transmitted from the back surface through the transparent material. The detector reads the level of reflected light from the recording layer on which the dots are formed and monitors the dot formation.

Another known thermal recording method uses a thermal transfer ribbon, as opposed to recording on a thermal medium that includes an integral thermal recording layer. The ribbon includes a flexible base layer or soluble ink or marking layer applied to one side of the membrane. The ribbon is placed in contact with the ink receiving paper, i.e. plain paper, and the ink layer is in face-to-face relationship with the receiving paper. Next, the base is selectively heated from the back side. In an area where a temperature rise sufficient to melt or liquefy the ink is given, ink transfer occurs and marks or dots are formed on the paper.

The main advantage of this type of recording device is that it uses ordinary cheap paper as the receiving paper and does not require the use of expensive special thermal paper.

To perform high quality toner image recording using thermal transfer technology,
Precise control of pixel density (dot size) is important. Therefore, it is highly desirable to incorporate dot monitoring and feedback control concepts into thermal transfer image recording devices.

Some known thermal transfer devices use resistive element print heads that heat in response to the application of electrical current. The head engages with the back surface of the ribbon to apply thermal energy, melt the ink through the base, and transfer. Dot formation occurs between the opaque receiving paper and the generally opaque ribbon and cannot be visually monitored. However,
Even if dot formation is seen from the back side of the ribbon, it is difficult to monitor dot formation with a photodiode for feedback purposes because of the overlapping print heads.

Before integrating the feedback control concept into the thermal transfer recording device, two problems must be solved. First, a visual indicator must be provided so that the ink transfer or dot size can be monitored from the back side of the ribbon. Second, the optical path between the visible indicator and the photodetector must be unobstructed by elements that act on the backside of the ribbon and heat it.

As another method of selectively heating the thermal transfer ribbon by an external thermal energy applying device, such as a resistive element printing head, some known thermal ink ribbons include an electrically resistive layer in their multilayer structure which acts as an internal heating element. There is. In use, a recording signal voltage is applied between a pair of isolated electrodes that contact the back surface of the ribbon. This produces a current in the resistive layer between the electrodes. Heat is generated in the resistance layer by the electric current, and the heat is transferred to the ink layer for transfer.

For representative examples of resistive layer thermal transfer ribbons, thermal recording devices and components adapted for use with them, see US Pat. Nos. 4,477,198; 4,470,714;
See 4,458,253, 4,345,854 and 4,329,071. Also, IBM
Technical Dice Closure Biuretin, 1976
See also "Thermal Transfer Printer Using Current-Pulse Heating Specialty Ribbon", Vol. 18, No. 8, p. 2695, January.

The U.S. Pat. No. 4,345,845 relates to a feedback controller in which the electrodes are driven by a voltage source rather than a constant current source.
This device uses an electrical signal for feedback that represents the internal ribbon voltage at the print point. However, this patent does not attempt to provide a visual indicator that represents or is proportional to pixel density or dot size.

It is also known to provide an integral resistance layer in the electrothermal recording paper used in facsimile machines. Typically, such papers have a base or support layer made of paper, a conductive layer on the base layer having sufficient resistivity to generate juule heat in response to an electric current flowing therethrough, and the top of the exothermic conductive layer. It consists of a heat-sensitive recording layer which is somewhat conductive and is applied to the. A recording signal voltage is applied between the spaced electrodes in contact with the top recording layer. The relative resistivity values of the recording and conductive layers are such that current flows from the first electrode through the recording layer to the underlying conductive layer, laterally along the conductive layer to the second electrode, and then through the recording layer to the first. It is designed to return to the second electrode. The current in the conductive layer generates heat which flows toward the upper recording layer, discoloring or modulating the thermal dye inside to produce visible marks or dots.

For representative examples of recording paper having an internal conductive heating layer coated with a conductive and thermal reaction recording layer, see Tappi, 19
1983, Vol. 59, No. 10, pp. 92, 93. Shimotsuma et al., "Electronic thermal recording paper and U.S. Pat. No. 4,133,933, 3,95.
See 1,757 and 3,905,876.

One advantage of folding the resistive heating layer onto a thermal transfer ribbon or thermal recording paper is that the recording dots are formed between the electrodes so that the recording dots are formed in an area that matches the spacing between the two electrodes using a pair of electrodes separated from each other. A signal is added. The spacing between the electrodes is not blocked by conventional external printing heads, and thus serves as a "window" for optically monitoring the indicators of dot formation and ink transfer.

As mentioned above, it is highly desirable to incorporate dot formation monitoring and feedback control into the recording device to substantially improve the quality of the toner image produced by thermal transfer recording. However, the known thermal transfer ribbon cannot apply optical observation or feedback by giving a visible index of dot formation or ink transfer on the back surface of the ribbon, so that this technology cannot be applied.

Thus specially constructed to improve the quality of the thermal transfer recording of tones or gray scale images on the receiving paper,
It is an object of the present invention to provide a thermal transfer medium such as a thermal transfer ink ribbon.

It is also an object of the present invention to provide a thermal transfer medium adapted for use in a thermal transfer recording device that uses optical monitoring and feedback to more accurately control the recording dot size or pixel density.

It is also an object of the present invention to provide a thermal transfer ribbon that includes a soluble ink layer on one side of the ribbon and a visible indicator of ink transfer and / or dot formation on the opposite side of the ribbon.

It is also an object of the present invention to provide a thermal transfer ribbon that includes an integrated resistive heating layer that heats in response to the passage of an electric current for the purpose of dissolving ink on one side of the ribbon and activating a heat-sensitive visual indicator on the other side of the ribbon. Is the purpose.

The present invention provides a thermal transfer medium, preferably ribbon-shaped, which is particularly suitable for use in a thermal transfer image recording apparatus which uses dot size or pixel density monitoring and feedback control to improve the quality of recorded tones or gray scale images.

The thermal transfer ribbon embodying the present invention comprises, as basic elements, a thermal transferable ink layer, a heat sensitive indicator layer, and a resistance heating element layer, and may further include one or several layers.

The function of the resistive layer is to generate thermal energy in response to the current flowing through it. It is placed in thermal communication with them on both sides of the ink and indicator layers. The thermal energy generated in the resistance layer flows to the ink layer and is activated by changing the ink from the non-transferable state to the transferable state, and further flows to the indicator layer, and at the corresponding or corresponding portion, the ink layer on the opposite side of the ribbon. It forms an optically detectable indicator that is proportional to ink activation.

Typically, the ink layer will be over the entire surface of the ribbon structure and will be placed in contact with an ink receptive image recording paper, such as white plain paper. The indicator layer is on the back side of the ribbon and the resistive layer is located in the middle of the ribbon structure between the ink and the indicator layer.

Preferably, the indicator layer is also somewhat conductive and an image recording signal applied between a pair of spaced electrodes in contact with the indicator layer causes a heating current to flow in the resistive layer portion between the two electrodes. The generated heat melts or melts the ink on the front surface and transfers it to the paper, and forms an optically detectable index mark in the index layer between the two electrodes. The index mark is proportional to the activation of the ink and thus provides an indication of the dot size or pixel density that will be formed on the receiving paper by the transfer of the ink.
The index mark is monitored by a photodetector, which generates a monitor pixel density signal and sends it to the recording transfer controller, where it is compared to the target or desired density signal. Based on the comparison, the device regulates the application of the heating current to the resistive layer until a predetermined comparison value is reached, whereupon the application of the current is terminated.

[Example] A thermal transfer medium embodying the present invention is schematically shown in FIG. 1 in the shape of a thermal transfer ribbon 10. Ribbon 10 is a multi-layer structure or stack and comprises, from bottom to top, a thermally transferable ink layer 12, an electrical resistance heating element layer 14, and a heat sensitive / electronic conductivity indicator layer 16.

In FIG. 2, the ribbon is placed in operative engagement with the ink receptive image recording paper 18. The recording paper 18 is white or colored plain paper or other sheet material, and is configured to be able to receive the ink thermally transferred from the layer 12.

For convenience of explanation, the ink layer side of the ribbon 10 configured to engage with the sheet 18 is referred to herein as the front side. In this way, the indicator layer 16 becomes the back surface of the ribbon 10 and the resistive layer 14 is located in the middle of the ribbon stack between the front layer 12 and the back layer 16.

The index layer 16 is contacted with a pair of spaced electrodes 20 and 22 for ink transfer. Generally, the inter-electrode spacing is determined by the maximum size of dots or marks recorded on the sheet 18. For a resolution of 80 dots / cm (200 dots / inch), the maximum dot size is approximately 0.125 mm (0.005 inches) and the electrodes 20 and 22 are positioned accordingly.

The first or signal applying electrode 20 is electrically connected to a recording signal output terminal that outputs a recording voltage signal Vs of a sub-control device 24 of the thermal transfer recording device described later. The second or counter electrode 22 is connected to the return terminal of the sub-control device 24,
It is set to a common ground potential.

In response to the application of the recording signal V _s , the electrode 2 is moved through the ribbon structure, as indicated by the current path indicator line I with the current direction arrow.
0 through the conductivity indicator layer 16 to the lower resistance layer 14, layer 1
A current path is established along 4 to the counter electrode 22, then through the layer 16 to the counter electrode 22 again.

Heat is generated in this region by the current flowing through the portion of the resistance layer 16 between the electrodes 20 and 22. Layer 14 is in heat-conducting relationship with layers 12 and 16, and heat is transferred up and down to produce a heat-activated reaction at the coincidence of layers 12 and 16 on both sides of layer 14.

In response to heat input from layer 14, the ink on the facing side of layer 12 melts or changes from solid to liquid and forms paper 18
Is transferred to. At the same time, a part of the heat is transmitted to the indicator layer 16 to activate the thermal dye inside the indicator layer 16 to change the color, and the optical size proportional to the dot size, that is, the pixel area density, formed on the paper 18 by the transfer of the ink from the layer 12. A dot or mark that can be detected is applied to the back surface of the ribbon 10.

The ribbon 10 incorporates an indicator layer to provide a visible or optically detectable mark, which is sensed by an optical monitoring device such as the photodetector 26 shown in the diagram. Preferably, photodetector 26 measures the level of light reflected at the portion of layer 16 between electrodes 20 and 22 and sends this information to sub-controller 24 for more precise dot size control in the manner described below. Used for.

The ribbon structure embodying the present invention has several advantages. First, it provides an indication of dot formation on the back of the ribbon that is accessible for monitoring. This is necessary because the actual dot formation occurs at the ink layer-receiver paper interface where viewing is hindered by the opacity of the receiver paper 18 and ink layer 12. Second, by providing a resistive layer inside the ribbon structure, heat can be generated using spaced apart electrodes located outside the edges of the layer 16 area where the index marks are formed. . In this way, the electrodes do not obstruct the index marks as in the case of conventional external heat generating print heads configured to engage the backside of the thermal transfer ribbon.

In the three-layer ribbon 10 shown, the resistive layer 14 is not only a resistive heating element that performs ink transfer and activates the thermal dyes in the layer 16 to form corresponding index marks or dots, but also the flexible support of the outer layer 12. Work as a body.

Preferably, layer 14 is a polymer or resin film that is loaded with conductive carbon particles to reduce the high resistivity of the film to a low resistance value and sufficient current at a fairly low signal voltage to cause sufficient ink transfer and indicator layer 16. Generates the amount of heat required to activate the thermal dyes therein.

As an example of a resistance layer material suitable for use in the ribbon 10,
Included are polymers that are a blend of polycarbonate membranes with conductive particle carbon black and aliphatic polyurethane and urethane acrylic copolymers with conductive particle carbon black. These materials are described in U.S. Pat. No. 4,477,19.
No. 8 and various other patents and technical references cited therein.

Also, the resistive layer 14 itself is US Pat. No. 4,470,
It may be in the form of a laminate consisting of a polymer support film such as Mylar having an inorganic resistance material coating such as a metal silicide as described in No. 714.

Typically, the resistive layer 14 has a thickness in the range of 0.01 to 0.02 mm, and the front surface is typically 0.002 to 0.008 mm.
A soluble thermoplastic or wax-based ink or marking layer 12 having a thickness in the range of .about. Official representative examples of ink layers that can be used in ribbon 10 are U.S. Pat. Nos. 4,477,198 and 4,3.
84,797 and various patents and technical references cited therein.

The index layer 16 on the backside of the ribbon 10 has two required properties. First, the layer 16 is made to flow with sufficient current for the layer thickness.
Electrodes 20 and 22 in contact with the outer surface of the lower resistance layer 14
It must be sufficiently conductive to establish a current path I in between. Also, the material composition should be heat activated in response to heat generated by the current in resistive layer 14 to produce visible or optically detectable marks on the backside of the ribbon.

One type of material suitable for use in the indicator layer 16 is a polymer binder in which a heat sensitive indicator component for providing an indicator function and a conductive component for reducing the resistivity of the layer and allowing sufficient current flow are dispersed. I'm running.

Typically, the heat sensitive indicator component can take the form of Leuco type dyes that are widely used in heat sensitive recording paper. The conductive component can take the form of a metal iodide such as cuprous iodide. For a comprehensive description of the various ingredients that can be incorporated into indicator layer 14, see US Pat. No. 3,905,905.
876, No. 3,951,757 and No. 4,133.
See 933. In addition, the above described double. See also "Electronic Thermal Recording Paper" by Shimotsuma et al.

For purposes of explanation, the ribbon 1 between electrodes 20 and 22 is shown in FIG.
A pixel area portion PA extending in the horizontal direction of 0 is shown bounded by vertical dotted lines 28 and 30. The corresponding parts of the individual layers in the PA part are designated as 12a, 14a and 16a. The corresponding pixel area part of the paper 18 on which the dots are formed is
Denote by a. The PA part represents the pixel area part of the ribbon 10 which is affected when the current path I is established, and the actual size and shape of the pixel area part PA is undoubtedly somewhat different from the part delimited by the lines 28 and 30. Please understand that it is different.

A preferred use of ribbon 10 is to provide a pair of electrodes 20 and 22 having substantially equal surface area edges 32 that contact the outer surface of layer 16. This induces a substantially constant current density in the portion 14a of the resistance layer 14 when the current path I is established, and the heat generation is not concentrated near one of the electrodes P
It is done so that it is somewhat uniform over the width of section A.

Before the ink in layer 12 melts, it must be heated to the minimum activation temperature. Similarly, the dye in indicator layer 16 does not discolor until the minimum activation temperature is reached. Preferably, the compositions forming the ink layer 12 and the indicator layer 16 are formulated so that their respective minimum activation temperatures are the same or at least close to each other.

In response to the amount of heat transferred from the portion 14a sufficient to obtain the minimum activation temperature, a part 34 of the ink in the portion 12a is melted and transferred to the paper portion 18a, and marks or dots 36 are formed on the portion.
And a portion 38 of the heat-sensitive indicator layer in the corresponding pixel area portion 16a is discolored to cause visible or optically detectable dots or marks 4 between the electrodes in the visual field of the photodetector 26.
Form 0. The size of the index dot 40 is proportional to the size of the transfer dot 36 because the reactions in sections 12a and 16a are triggered by a common heat source. The proportionality or density ratio of the two dots is determined by empirical testing to obtain a calibration factor which is added to the photodetector reading to add the actual size of dot 36 or the pixel area on paper 18 that forms dot 36. The density of the portion 18a is calculated.

Unlike prior art thermal transfer devices designed primarily to produce uniform sized dots for use in binary (black and white) recording applications such as dot matrix characters and google symbols, the ribbon 10 varies dot size or pixel density. It is designed for use in devices capable of recording tones or grayscale images. The size of the thermal transfer dots 36 and the corresponding index dots 40 is a function of the amount of heat applied to form the dots. That is, the dot size gradually increases with the amount of heat applied to form the dot.

Due to the initial dissolution of the ink in part 12a and the corresponding activation of the thermal dye in the corresponding pixel area part 16a, (P
Small initial dots 36 and 40 (compared to surface area A)
Is formed. In response to continuous heat input, the dots gradually increase in area, or "grow". When the heat input ends, the dot grows a little larger due to the residual heat in the ribbon 10, but the growth starts there. When the heat input is restarted, the dot growth is restarted when the minimum activation temperature is reached. Dot growth continues until a full size dot is formed that is approximately equal to the surface area of the PA section. Outside the boundary of the PA section, the temperature drops to a point below the minimum activation temperature, and automatically increases any further increase in dot size despite the fact that current may still be flowing in the current path I. Ban to.

In this way, the recording dots 36 and 40 start small and gradually increase in size as the amount of heat applied to form the dots increases. The heat can be applied continuously,
In this case, the heat input ceases, i.e., the dot size is ramped up uninterrupted until the dot reaches full size, or the dot size is ramped up by applying a series of signal voltage pulses to produce the corresponding heat input pulses. You can also do it.

The illustrated ribbon 10 has three basic layers 12, 14 and 16
Although described as having only one, the ribbon structure can optionally include additional layers without departing from the spirit and scope of the present invention. Such optional layers may be between the resistive layer 14 and the ink layer 12 and / or the resistive layer 14 and the indicator layer 16.
It is thought to be placed between. Functionally, such an optional layer facilitates ink transfer (eg, by providing an ink release layer next to the ink layer 12) and / or enhances thermal transfer from the resistive layer 14 to the two outermost layers 12 and 16. Concentrate.

A fourth thermal transfer image recorder 42 specially configured to record a toned image on the receiver paper 18 using the ribbon 10.
It is shown diagrammatically in the figure. The illustrated device 42 is a line recording type in which the pixel area lines defining the desired image are recorded sequentially.

The various components of the device 42 are supported on a horizontal base member 43 having a feed through groove 44. The recording paper 18 in the form of white plain paper is supplied from a roll 46 supported on the base member 43. The roll 46 and the paper 18 are supported by a pressure roller or platen 48 placed on one side of the groove 44 and a print head assembly 50 on the opposite side of the groove 44 (extending between a supply reel and a take-up reel not shown). Present) and a fixed length ribbon extending in the lateral direction. Under the assembly 50, the paper 18 passes through the groove 44 and meshes with a pair of paper advance or line index rollers 51 and 52. A collection of these elements supports the paper 18 in the image recording operating position.

As shown in FIG. 5, the print head assembly 50 has a plate-like support 53 made of an electrically insulating material. Support 53
A laterally extending elongated groove or opening 54 is formed therein to define a "window" in which the free ends of the plurality of signal electrodes extend in mating relationship with corresponding plurality of spaced counter electrodes 56. To do.

Each electrode has a separate electrical contact, the opposite end of which is connected to a printhead signal processor and matrix switching device 57 operated by a power supply 58 controlled by the controller 24. Ribbon 10 is member 53
The free ends of the electrodes 55 and 56 supported above and overlapping the window 54 are adapted to engage the indicator layer 16 on the backside of the ribbon 10.

In order to print dots or marks in the pixel area A between the first two electrodes, the recording signal V _s is applied to the first signal electrode 55a paired with the first reflective electrode 56x.
That is, the print head signal processor 58 operates the matrix switching device 57 to apply V _s to the electrode 55a, and the opposite electrode 56x drops to the ground potential with respect to V _s , and a current path I is established between the two to establish resistance. Heat is generated in the corresponding portion of layer 14. To selectively print dots in the next pixel area B, a signal voltage V _s is applied to the electrode 56b paired with the first counter electrode 56x. Dot printing is then performed in the adjacent pixel area C by, for example, pairing the second signal electrode 56b with the next counter electrode 56y. Further electrode pairs (not shown) are provided for the entire length of the groove 54. Appropriate software and matrix switching techniques can be used to individually access the electrode pairs corresponding to each pixel area in the line.

In front of the printhead assembly 50 in engagement with the viewing window defined by the groove 54, is located a photocell detector or sensor 26 for optically monitoring the density of each pixel area in the current row of recording. ing.

Preferably, the detector 26 is configured with adjacent electrode pairs 5 on the assembly 50.
It has a linear array of photodiode lines (denoted by 60 in FIG. 4) which have the same number and spacing as 5 and 56 and receive the reflected light from the corresponding pixel area of the layer 16 between the electrodes. However, if the size and spacing of the photodiode 60 is different from the electrode pair, the photodiode 60
It is desirable to provide adaptive optics between the row and viewing window 54 to maximize the efficiency of the dot monitoring process.

A type of commercial detector 26 suitable for use in device 42
The photodiode array, which is a G series image sensor manufactured by Reticon, has a pitch of about 40 / mm (1000 / inch). 8 pieces / mm (200 pieces / inch)
When used with the printhead assembly 50 having .about. Electrodes, the pixel area is five times larger than the photodiode area, which means that the photodiode cannot "see" the entire pixel area. This condition can be corrected by placing an objective lens 62 in the optical path that acts to provide a focused image of a large pixel area to a small sized photodiode.

Although ambient reflected light levels from the portion of layer 16 that engages groove 54 can be sensed, supplemental illumination of this area is desirable for improved efficiency and consistent, reliable density readings. desirable.

In the exemplary embodiment, the device 42 includes an illumination source 64 in the form of a lamp 66 and associated reflector 68 located on the upper front of the assembly 50 to direct light onto a strip of layer 16 that engages the viewing window 54. . Since the photodiode is extremely sensitive to infrared wavelengths, a lamp 66, such as a fluorescent lamp, which emits less infrared radiation, is preferably used to prevent the photodiode from being overloaded by out-of-band energy in the visible band that carries pixel density information. To do. Also, if the selected lamp 66 contains a significant infrared component in the spectral output, an infrared blocking filter 70 (shown in dotted lines) in front of the photodiode 60.
Can be placed arbitrarily to minimize false readings.

In FIG. 4, the functional elements of the controller 24 are shown in a block diagram within the dotted box.

In order to record a black and white image on the sheet of paper 18, electronic image data input signals that determine the pixel-wise density of the image matrix are sent to a device for receiving these signals, such as a gray scale reference signal buffer memory 72. Preferably, the image signal is in digital form provided by an image processing computer or digital data storage device such as a disk or tape drive. If the electronic image signal was originally recorded in analog form from the video source, it is preferably analog-to-digital converted in a known manner before being transmitted to the buffer 72. Further, as described above, the control device 24 may optionally include an analog / digital signal conversion device that directly receives an analog video signal and converts it into a digital format within the control device 24. Preferably, the buffer 72 is a full frame image buffer that stores the entire image, but it can also be configured to receive a portion of the image signal in sequence, so that the buffer 72 only receives one or two rows of the image. It may also have a small memory device to hold.

In this way, the controller 24 includes an electronic image signal receiver which uses the signal as a gray scale reference signal to determine the desired or target pixel density, which is output from the optical monitoring photodiode detector 26 in the feedback loop. Compare with the density signal.

The operation of the controller 24 is coordinated with respect to the system clock 74, which among other things sets the timing of sequential reading of the light level or pixel density signal from each photodiode 60 in the linear array. The light level signal from the detector 26 is sent to a photodiode signal processor 76 where the analog signal is converted to digital form. Further, this A / D conversion can be performed by a sub device incorporated in the detector 26.

The density signal from processor 76 is sent to signal comparator 78 along with the reference signal from buffer 72 and a signal indicative of the comparison is sent to print decision logic 80. Based on the comparison information, device 80 provides a print command or cutoff signal for each pixel in the current row. The print command signal is sent to the heat input duration determination logic unit 82 and the abort signal is sent to the pixel status signal unit 84.

When a print command is received, the logic unit 82 uses an internal look-up table to set the excitation time for each electrode pair to be excited and send this information to the print head signal processor and the power supply 58 and follow these instructions. Excite the selected electrode.

The abort signal of the pixel state logic 84 keeps track of which pixels are being recorded and what additional heat input needs to be applied. Upon receipt of the abort signal for each pixel in the current row being printed, logic unit 84 provides an output signal to line index and system reset unit 86.

The reset device 86 sends a first output signal 90 to activate a step motor (not shown) to drive the paper feed rollers 51 and 52 to incrementally advance the paper 18 by one line and record the next additional line. Get ready. Signal 90 also activates another stepper motor (not shown) to drive the ribbon take-up reel and supply a new fixed length ribbon 10 onto window 84. In addition, the reset device 86 receives the reset signal 9
2 is sent to reset the components of the control device to prepare for recording the next line.

In the case of the elongated photodiode array 60, it is quite possible that the output and sensitivity of the individual photodiodes 60 will fluctuate somewhat. However, it is possible to compensate for such fluctuations by checking the fluctuations by factory calibration and easily adding correction factors for the shape of the calibration software program. Similarly, variations in the voltage output characteristics of each electrode pair within the printhead assembly 50 are determined by calibration measurements and the excitation times of the individual electrodes are automatically adjusted to provide uniform voltage output across the array. It can be modified by a software program.

To activate the recording device 42, the print decision logic 80
To start the thermal recording cycle. The activation is completed by the operator manually activating an activation button (not shown).

In response to the activation of print decision logic 80, a grayscale reference signal indicative of the desired or target density of all pixels in the first row is sent from buffer 72 to logic 80.
Logic unit 80 evaluates this information and for those pixel areas that do not record dots, a truncation signal is sent to pixel state logic unit 84 to represent the brightest tone in the gray scale. A print command signal for the pixel area stamping the dots is sent from the logic unit 80 to the heat input duration determination logic unit 82. The logic unit 82 uses a look-up table to output an initial heat input duration signal indicating the time each electrode pair is excited to print the initial dot 36 in the corresponding pixel area PA on the sheet 18 of the layer 16. The corresponding index mark 40 is formed in the corresponding pixel area portion.

To minimize the line recording cycle length, it is desirable that the initial dot be smaller than the minimum dot size, but large enough that the number of continuous thermal energy applications required to produce the desired size dot is not excessive.

For example, the logic device 82 outputs an initial heat input time signal forming an initial dot 36 and corresponding index mark 40 which is 75% to 85% of the final or desired dot size. This means that each of the initial dots is smaller than the pixel area that forms it. Even if the reference signal indicates to record a high density dot that substantially fills the pixel area, a small dot is first formed to trigger the formation of the optically detectable index mark 40. , Used in a feedback loop for precise control of dot size and pixel density.

Initial duration signal is sent from logical unit 82 to the print head signal processor and power feeding source 58, it thereto during the initial is indicated by the address of each of the electrode pairs in print head assembly 82 time signal voltage V _s Add.

The selected electrode pairs 55 and 56 are the indicator layer 16 on the back surface of the ribbon 10.
A voltage V _s is applied to the heat generating current to the corresponding selection portion of the resistance layer 14. In response to this heat, the ink in the portion of the layer 12 corresponding to the selected pixel area is melted and transferred to the paper 18 to form an initial dot 36 in the selected pixel area, and the thermal sensitivity in both corresponding pixel area portions of the layer 16 is established. The dye is activated to form a corresponding initial index dot or mark 40 proportional to dot 36. The initial index dot 40 is visible through the groove or window 54 and the density or reflected ray level of each corresponding pixel area PA of the layer 16 between adjacent electrodes is read by the photodiode 26. These density signals indicative of the pixel density on the paper 18 are sent to a signal processor 76 from which a pixel density signal index is sent to a comparator 78 which compares the initial pixel density with a target density signal sent from a reference signal buffer 72. To do.

Correlation of the photodiode output signal with the reflective properties of the back layer 16 of any particular type of ribbon 10 establishes a reference signal value for the lowest reflectance, ie, the highest reflectance, indicating the brightest pixel in the gray scale, by performing a test reading on the blank ribbon 10. You can do it. Further, before the printing head is excited to record the initial dot 36 and the corresponding index mark 40, the photocell reading of the corresponding pixel area portion PA on the phase 16 which engages with the observation window 54 is automatically recorded in the recording device 42. By doing so, the setting of the reference value can be incorporated in the recording cycle.

As noted above, residual heat that contributes to the thermal inertia of the ribbon structure may cause further dot and index mark growth following deenergization of the electrode pairs within the printhead assembly 50. Therefore, it is desirable to delay the photodetector reading shortly after the electrode pair is deenergized to include any spurious growth in this reading.

The pixel density reading is compared with a reference signal by a comparator 78 and a signal indicative of the difference between the two is sent to print decision logic 80. Since the initial dot size has been calculated to be smaller than the final dot size, most difference signals indicate that more heat input is required to make each dot somewhat larger. However, the thermal recording parameters fluctuate, so the initial heat input is 75-8 of the desired size.
It is designed to produce 5% of the dots, but at least some of the dots may reach the desired size. For these pixels, print decision logic 80 sends a cutoff signal to pixel state logic 84 to terminate the application of further heat input during the next part of the recording cycle.

For pixels that do not reach the target or desired density,
Print decision logic 80 issues a print command to duration decision logic 82 from which it outputs a signal indicating the time required to grow more dots. Since the current goal is to make the dot somewhat larger than the initial size, the excitation duration of the electrode pair will be less than the time used to record a large initial dot.

After the selected electrode pair is energized and after a short delay for thermal stabilization, the photodiode 60 again reads the reflected light level from the layer 16 and sends a signal back to the comparator 75, with these readings relative to the reference value. Find out. Again, the print decision logic unit 80 recycles in this way, and a cutoff signal is sent to the dots that have reached the target size, and a print command is sent to the pixel areas that require more heat input to reach the density of the target value. To be done. When the pixel state machine 84 indicates that all pixels in the row are at the target density, the pixel state logic 84 triggers the line index and reset device 86 to move the paper incrementally by one row and advance the ribbon 10. Various control elements reset and prepare to record the next image line.

In this way, a typical line recording cycle senses the reflected light level of the corresponding pixel area portion of layer 16 engaging the viewing window to establish an initial reference level indicative of the lowest density pixel, Recording an initial dot in the selected pixel area that is smaller than that required to excite the selected electrode pair according to the grayscale reference signal to obtain the target density, and add a dot due to heat accumulation and thermal inertia after the delay. Ribbon 1 on which index dots 40 are formed by growth
0 The step of measuring or observing the density of the initial dots by sensing the reflected light level on the back surface, the step of comparing the observed density with the target density, and the step of setting a large dot as the target density based on this comparison Starting the application of additional heat energy to the pixel area and terminating the input of further heat energy to the pixel area, which indicates that the comparison has reached a predetermined comparison value.

For example, if the monitored density is very close to the target density,
For example, in the range of 92-98% of the target value, it is very difficult to adapt the next round heat input to the pixel area of the ribbon to do the very small amount of additive growth needed to reach the target density. Is. Therefore, it is desirable to end the ignition of further thermal energy to that particular pixel area, rather than risking the creation of dots that are as large as necessary to match the target density exactly.

In the above process, desired dots in each pixel area are formed step by step. First, the initial dots are made and layer 16
Corresponding pixel area portion is measured and compared with a gray scale reference signal, and if necessary, one or more short thermal energy pulses are sequentially applied to the pixel area to achieve the target density. Feedback allows the dot size to be controlled to a much higher degree than if the device were simply operated in open loop and is correlated with the duration of thermal energy for each pixel area.

As an alternative to the stepwise mode of operation, the recording device 42 can be calibrated to provide continuous power supply with feedback monitoring of dot formation. In this case, the pixel area P in the row with dots recorded according to the grayscale reference signal
All electrode pairs corresponding to A are turned on at the same time. As the index dot 40 develops and continues to grow, the pixel density is continuously monitored and compared to a reference value. When a predetermined comparison value is reached for a given pixel area, the device will automatically deactivate the corresponding electrode pair. This operation mode shortens the recording cycle to some extent as compared with the stepwise dot formation cycle. However, since the control by the feedback loop does not consider the additional growth of the dot and the index mark due to the thermal inertia of the ribbon 10, the control of the dot size is performed. The degree is not so great. A certain amount of additive growth can be expected and at a given low comparison value the heating element can be turned off to compensate somewhat for this additive dot growth.

However, unless there is an urgent need to reduce the recording cycle time, high accuracy is desirable with the stepwise method.

Although the embodiment of the recording device 42 is shown as a line recording device, a scanning mode for performing image recording by moving the print head assembly 50 and the photodetector 26 narrower than all the associated rows back and forth across the width of the paper. It is also within the scope of the invention to modify the device for operation. In addition, the print head assembly and the photodetector are configured to record one or more lines or record the entire image to minimize the need for relative motion between the components of the recording device and the thermal recording medium. Or it can be resolved.

In the exemplary embodiment, sensing and monitoring of the indicia mark 40 is performed by a photoelectric photodetector operating in the visible light band, but the device may be modified to use other types of detectors operating at other wavelengths (e.g. It is within the scope of the invention to include other types of structures (such as fibers) to monitor the recording pixel density.

All of the matter contained in the above description and accompanying figures is for the purpose of description and limitation, as the thermal transfer ribbon, recording device and method may be modified or altered within the spirit and scope of the present invention. Not a thing.

[Brief description of drawings]

FIG. 1 is an elevational view of a thermal transfer recording medium embodying the present invention in the shape of a thermal transfer ribbon, and FIG. 2 is an elevational view showing the front surface of a ribbon engaging with recording paper and a pair of a pair of engaging with the back surface of the ribbon. FIG. 3 is a diagram similar to FIG. 2 showing an ink dot provided from an ink layer on the front surface of the ribbon and an index mark formed on the back surface of the ribbon, and FIG. FIG. 5 is a diagrammatic view of a thermal transfer recording apparatus configured to use the ribbon of FIG. 5, and FIG. 5 is a partial plan view of a print head assembly which is one element of the recording apparatus of FIG. Explanation of reference numerals 10 ...... Ribbon 12 ...... Front layer 14 ...... Resistive layer 16 ...... Back layer 18 ...... Image recording paper 20, 22, 55, 56 ...... Electrode 24 ...... Sub-control device 26 ...... Light detection Device 42 ... Thermal transfer image recording device 46 ... Roll 48 ... Platen 50 ... Printing head assembly 51, 52 ... Line index roller 53 ... Support 57 ... Switching device 60 ... Photodiode array 62 ... Objective Lens 64 ... Illumination source 66 ... Lamp 68 ... Reflector 70 ... Infrared blocking filter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B41J 31/10 9012-2C 35/36 9012-2C B41M 5/26 8305-2H B41M 5/26 M

Claims (10)

[Claims] 1. A thermal transfer ink layer, a heat-sensitive index layer, and a resistance layer that generates heat in response to a flowing current, the resistance layer being disposed in a thermal conductive relationship with both of the ink and the index layer, The heat generated in the layer flows to the ink and the indicator layer to activate the ink in the ink layer and to the corresponding portion of the indicator layer in which an optical transfer proportional to the ink transfer from the ink layer. A thermal transfer ribbon that forms a detectable index mark on the surface. 2. The thermal transfer ribbon according to claim 1, wherein the ink layer is supported on one surface of the resistance layer and the indicator layer is supported on the opposite surface of the resistance layer. 3. The indicator layer according to claim 2, wherein the indicator layer is conductive, and an indicator is applied from one of the electrodes by an electric signal applied between a pair of spaced electrodes in contact with the indicator layer. A thermal transfer ribbon in which a current path is established through a layer to the resistive layer, towards the other electrode along the resistive layer and then back through the indicator layer to the other electrode. 4. The ink layer of claim 3, wherein the ink layer is constructed to be placed in engagement with an ink receiving paper, the ink layer is soluble and the ink is The thermal transfer ribbon which is melted in response to the application of heat and is transferred to the receiving paper arranged in the engaging relationship to form dots thereon. 5. The thermal transfer ribbon according to claim 4, wherein the indicator layer contains a heat-active component that discolors in response to heat applied from the resistance layer to form the indicator mark. 6. The ink layer of claim 3, wherein the ink layer is adapted to be placed in engagement with an ink receiving paper, the ink layer is soluble, and the ink is from the resistive layer. In response to the application of heat, it melts and is transferred to the receiving paper arranged in the engaging relationship to form dots thereon, and the indicator layer discolors in response to the heat applied from the resistance layer. The dot formed on the receiving paper and containing the heat-active component for forming the index mark, and the index mark correspondingly formed on the index layer, increase in size as the amount of heat from the resistance layer increases. A thermal transfer ribbon that is designed to do. 7. The thermal transfer ribbon according to claim 1, wherein the resistance layer is made of a polymer film, and the polymer film contains a conductive component for lowering its specific resistance. 8. The indicator layer according to claim 1, wherein the indicator layer comprises a polymer binder, and the polymer binder reduces the specific resistance of one or several thermal dyes and the binder to make the binder conductive. A thermal transfer ribbon in which one or several components are dispersed. 9. The ink layer according to claim 1, wherein the ink layer is provided on the front surface of the ribbon and is arranged in an engaging relationship with a receiving paper to form a dot on the receiving paper by ink transfer. The dots are visually obscured by the receiving paper, while the indicator layer is provided on the back side of the ribbon, the indicator marks formed on it being visually distinct and optically detectable. Thermal transfer ribbon. 10. The index mark according to claim 1, wherein the index mark is formed on a part of the index layer facing the part where the ink is activated and transferred, and aligned with the part of the ink layer. Thermal transfer ribbon.